1. Field of the Invention
The present invention relates to a line test system for testing an access network (AN) through access nodes.
2. Description of the Related Art
Lately, both the digitization of subscriber lines and the use of fiber-optic cables in transmission lines have been promoted, and an access node has been introduced into an access network. Conventionally, in subscriber lines, wires from an exchange were directly connected to the telephone sets or terminal sets of subscribers. In such a conventional configuration, an area which can be covered by one exchange was limited since the transmission rate is often restricted and the length of the wire is also often restricted due to the degradation of signals. However, since by introducing a transmission system which is configured using digital lines, fiber-optics, etc. into a subscriber line, the transmission rate of a subscriber line can be increased and the degradation of signals can be suppressed, the length of a subscriber line can be extended and an area which is covered by one exchange can be extended. By increasing the capacity of an exchange, the number of exchanges can also be reduced.
FIG. 1 shows the basic configuration of an access network.
The access network comprises a subscriber set 1300, such as a telephone set, etc., a subscriber line 1301, an access node 1302 and a local exchange (LE) 1303. The access node 1302 includes a remote terminal (RT) 1304, a central terminal (CT) 1306 and a transmission line 1305 which connects the remote terminal 1304 and the central terminal 1306. RT1304 and RT1306 do not necessarily need to be connected in a one to one fashion; multiple RT1304 units can be connected to one RT1306. If RT1304 is provided with an interface through an exchange, CT1306 is not required, and a transmission line 1305 is sometimes directly connected to LE1303.
For the interface between the access node 1302 and LE1303, a standard interface which is set forth generally in ITU-T G. 965 or ETS300 347 is used, and is called a V5.2 interface.
In order to secure the reliability of accommodated subscriber lines, the conventional LE1303 is provided with a means for carrying out both a subscriber line test and a speech path test as line tests for an access network at regular or arbitrary intervals of time. If the access node 1302 is introduced into an access network, the target section of a speech path test between RT and LE is expanded and the importance of the test increases. The subscriber line test is an analog measurement by which the resistance of one pair of conductors, etc., is measured. In view of the nature of such tests, both a subscriber line test unit (SLT) 1304a and a speech path test unit (SPT) 1304b are mounted on RT1304. In this case too, test facilities similar to those of the subscriber line which is directly accommodated in LE1303 must be provided.
FIG. 2 shows the system configuration of a conventional access network.
Telephone sets 1400 shown in the upper part of FIG. 2 are directly accommodated in LE1402. But, telephone sets 1401 shown in the lower part of FIG. 2 are accommodated in LE1402 through AN1403. Even if during maintenance on RT1404, an attempt is made to carry out the speech path test of a certain line using a local craft terminal (LCT) 1405, in the conventional system, a third party could call up on a line to be tested during the test, and the speech path test would sometimes be disturbed.
Maintenance personnel designate a line to be tested by using LCT1405, and instructs SPT1406 to start the speech path test. SPT1406 originates a call to a call back test unit (CST) 1407 and confirms the procedures of processes up to the establishment of a line. When the line is established, maintenance personnel carry out a voice test, and confirms the quality of the line. Then, maintenance personnel confirm the procedure of the call clearing process. When the line is established, CBT1407 records the telephone number of a calling party. A certain time period after SPT1406 call clearing, CBT 1407 originates and returns a call to SPT1406, and SPT1406 detects a ringing signal and confirms the procedure of a call termination process. After the establishment of the line, CBT1407 clears the call, and confirms the procedure of the process.
However, if from the time when SPT1406 completes the clearing process until the time when CBT1407 originates a call, a third party originates a call, the call arrives at SPT1406, which disturbs both the maintenance personnel engaged in the speech path test and the calling party (third party).
FIG. 3 shows the configuration of SPT1406.
A speech path test control unit 1504 controls the entire test procedure of the speech path test. The speech path test control unit 1504 receives calls originated from telephone sets 1401, etc., and controls a relay in order to execute processes, such as establishing a telephone line, etc. In order to carry out tests, the speech path test control unit 1504 includes a speech path test measurement unit 1500, a relay control unit 1501, a multi-frequency (MF) oscillator 1503, and a call control unit 1502. In a speech path test, first, an instruction to originate a call is issued from the speech path test control unit 1504 to the call control unit 1502. The relay control unit 1501 which receives the instruction from the call control unit 1502 closes a relay 1506 and acts on LE1402 so that the effect is the same as when the handset of the telephone set is lifted. Then, a dial tone is returned from LE1402, and it is confirmed by the speech path test measurement unit 1500 that a telephone number is ready to be inputted any time. Then, a call is originated to CBT1407 on the LE1402 side. At this point, either pulse dialing or tone dialing is selected. If pulse dialing is selected, the call control unit 1502 transmits a telephone number by turning the relay 1506 on/off under the control of the relay control unit 1501. If tone dialing is selected, the call control unit 1502 causes the MF oscillator 1503 to transmit the telephone number in an audio format.
As described above, in the conventional system, in a state where a line to be tested is temporarily returned to a normal (idle) condition after SPT1406 call clearing during the speech path test, SPT1406 cannot refuse to receive an incoming call from a third party, which disturbs both the calling party and SPT1406 and causes a problem in that an exact speech path test result cannot be obtained.
In the subscriber line test and speech path test of a subscriber who is directly accommodated in LE1402, LE1402 can operate its own incoming call control function, since those tests are carried out by LE1402. By using this incoming call control function, the subscriber line test of a subscriber who is directly accommodated in LE1402 can be smoothly carried out. Thus, in the case of the subscriber line test of a subscriber who is directly accommodated in LE1402, the test can be carried out in such a way that the test may not be disturbed by a third party.
Since an access network through a V5.2 interface has recently been introduced, the test can be carried out in the remote terminal of an access network which is installed remotely and not in an exchange (LE). As a rule and even in this case, the incoming call control function of the exchange should be operated during the test.
In particular, the introduction of an access network plays an important role in a speech path test. Since a speech path which is conventionally confined inside an exchange is extended to a remote terminal which is located remotely, it will suffer from a greater failure rate.